With Ubuntu 18.04 Canonical introduced new network management called Netplan. In nutshell Netplan allows to directly configure network and/or switch between two network configuration daemons networkd and NetworkManager. By default networkd is configured for Ubuntu Server and NetworkManager for Ubuntu Desktop.
Since you mentioned that you have installed GNOME desktop on your Ubuntu server chances are that your system is still using networkd daemon hence your desktop has no access to the network configuration. To grant managed access of your network to your desktop open /etc/netplan/01-netcfg.yaml or /etc/netplan/50-cloud-init.yaml configuration file and change it:
FROM:
# This file describes the network interfaces available on your system
# For more information, see netplan(5).
network:
version: 2
renderer: networkd
ethernets:
enp0s3:
dhcp4: yes
TO:
# This file describes the network interfaces available on your system
# For more information, see netplan(5).
network:
version: 2
renderer: NetworkManager
ethernets:
enp0s3:
dhcp4: yes
Once ready apply changes by executing:
$ sudo netplan apply
Related article: https://linuxconfig.org/how-to-configure-static-ip-address-on-ubuntu-18-04-bionic-beaver-linux
Hope this helps
Lubos